Write command and write data timing circuit and methods for timing the same

ABSTRACT

Circuits, memories, and methods for latching a write command and later provided write data including write command and write data timing circuits. One such timing circuit includes internal write command latch to latch an internal write command in response to write command latch signal. The internal write command latch releases the latched write command in response to the write command latch signal after a latency delay. The timing circuit further includes a write leveling flip-flop (FF) circuit and a write data register. One such method includes generating and latching an internal write command. The latched internal write command is released after a latency delay responsive to the memory clock signal. The internal write command is propagated over an internal write command path. Write data is captured and internal write command latched in response to a write clock signal. The captured write data is released to be written to memory.

TECHNICAL FIELD

Embodiments of the invention relate generally to semiconductor memory,and more specifically, to timing internal clock and control signals forexecuting memory commands in a high-speed memory clock system.

BACKGROUND OF THE INVENTION

In semiconductor memory, data is written to memory for storage untilread at a later time. Writing data typically involves issuing a writecommand to the memory and also providing the write data that is to bewritten to memory. The write data can be provided to the memory at atime after the write command is issued to allow operations internal tothe memory device to occur for the write command to be executed. Thetiming between the issuance of the write command and its write data tothe memory are related by “write latency.” As known, write latency isthe delay, in clock cycles, from the issuance of a write command to thelatching of the first write data. An example of typical write latency is12 clock cycles of the Clk signal.

Correct timing of internal timing signals generated in response toexternal command and clock signals is critical for proper operation ofthe memory. Complicating the generating of correctly timed internalsignals is the relatively high frequency of memory clock signals. Forexample, memory clock signals can exceed 1 GHz. Further complicating thematter is that multi-data rate memories can provide and receive data ata rate higher than the memory clock signal. With respect to writecommands, a write clock signal may be provided to the memory forcorrectly timing the rate at which write data is received by the memory.Correctly timing internal write operations relative to the receipt ofthe write command, write data, memory clock signal and write clocksignal is required to properly complete a write operation.

The traditional method of timing the write data with the memory clock ismodeling both the write clock path and the system clock path to have thesame propagation delay. With higher-speed clock signals, however, thepropagation delay of the clock paths may be on the order of severalclock cycles, thus, preventing write throughput from being optimized.Additionally, the propagation delay can often vary due to power,voltage, and temperature conditions. In cases where the memory clock isa lower frequency than the write clock, tight phase control between thememory clock and the write clock is necessary for correct operation,which is complicated by the total propagation delay time and thevariation in the delay due to power, voltage, and temperatureconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a write command-data timing circuitaccording to an embodiment of the invention. FIG. 1B is a block diagramof a write latency multiplexer of FIG. 1A according to an embodiment ofthe invention.

FIG. 2 is a block diagram of a data input circuit according to anembodiment of the invention.

FIG. 3 is a timing diagram of various signals during operation of thewrite command-data timing circuit and the data input circuit accordingto an embodiment of the invention.

FIG. 4 is a block diagram of a memory device including a writecommand-data timing circuit according to an embodiment of the invention.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the invention. However, it will be clearto one skilled in the art that embodiments of the invention may bepracticed without these particular details. Moreover, the particularembodiments of the present invention described herein are provided byway of example and should not be used to limit the scope of theinvention to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the invention.

FIG. 1A illustrates a write command-data timing circuit 100 according toan embodiment of the invention. The timing circuit 100 includes a memoryclock and command buffer and clock circuit 110. The buffer and clockcircuit 110 includes a command buffer 112 that buffers memory commandsignals Cmd and provides the buffered command signals CmdIBOut to acommand latch 114 that captures the CmdIBOut signals. The capturedCmdIBOut is provided to a command decoder 116 that decodes the CmdIBOutand generates internal device signals to carry out the decoded command.In the case for a write command, the command decoder 116 generatesinternal write command signals WriteCmdY.

The buffer and clock circuit 110 further includes a memory clock buffer122 that buffers the memory clock signal Clk and provides complementarybuffered memory clock signals ClkIBOut, ClkIBOutF to a command latch andbuffer model delay circuit 124. The model delay circuit 124 models thepropagation delay of the command latch and buffer 114. The command latchand buffer model delay circuit 124 outputs an internal clock signalClk2Dec to a command decoder model delay circuit 126, which models thepropagation delay of the command decoder 116. The Clk2Dec signal ispropagated through the command decoder model delay circuit 126 andprovided as a write latency multiplexer clock signal Clk2LatMux. In someembodiments, the Clk2LatMux signal has the same frequency Clk signal.The model delay circuits 124, 126 approximate the delay through thecommand latch and buffer 114 and the command decoder 116 so that theWritecmdY and Clk2LatMux signals are roughly synchronized.

A multi-phase write clock generator model delay circuit 128 coupled tothe memory clock buffer 122 is also included in the buffer and clockcircuit 110. The model delay circuit 128 provides a delayed clock signalClkTrkWClk4Ph<0> in response to receiving the ClkIBOut signal from theinput buffer 122. As will be explained in more detail below, the modeldelay circuit 128 models the propagation delay of a multi-phase clockgenerator for a write clock signal. The Clk and Cmd signals provided tothe buffer and clock circuit 110 are considered to be in a first clockdomain. That is, the Clk signal has a first clock domain frequency andthe Cmd signals are latched according to the first clock domainfrequency.

The timing circuit 100 further includes a write clock buffer and clockcircuit 130. The buffer and clock circuit 130 include a write clockbuffer 132 that buffers a write clock WClk and generates complementarybuffered write clock signals WClkIBOut, WClkIBOutF. The WClkIBOut,WClkIBOutF signals are provided to a multi-phase clock generator 134that generates clock signals having fixed phase relationships to oneanother. In some embodiments, such as the one shown in FIG. 1A, themulti-phase clock generator 134 is a four-phase clock generator thatgenerates quadrature clock signals WClk4Ph<0:3> in response to theWClkIBOut, WClkIBOutF signals. That is, the four-phase clock generator134 generates a 0 degree clock signal synchronized with the WClkBOutsignal, and further generates a 90 degree clock signal having a 90degree phase relative to the 0 degree clock signal, a 180 degree clocksignal and a 270 degree clock signal. In some embodiments, the clockfrequencies of the multi-phase clock signals are the same clockfrequency of the WClk signal. In some embodiments, the clock frequenciesof the multi-phase clock signals can be greater or lower than the clockfrequency of the WClk signal. Typically, the clock frequency of themulti-phase clock signals are the same clock frequency as the Clksignal.

The WClk signal provided to the buffer and clock circuit 130 is in asecond clock domain. In some embodiments, the second clock domain mayhave the same clock frequency as clock signals in the first clockdomain. In some other embodiments, the second clock domain may have adifferent clock frequency than clock signals in the first clock domain.For example, the WClk signal may have a clock frequency that is amultiple of the frequency of the Clk signal, such as twice the frequencyof the Clk signal.

The timing circuit 100 further includes a write enable timing circuit150. The timing circuit 150 includes clocked counter circuits 152, 154.The counter circuit 152 is clocked by the 0 degree clock signalWClk4Ph<0> from the multi-phase clock generator 134 and the countercircuit 154 is clocked by the ClkTrkWClk4Ph<0> signal from the bufferand clock circuit 110. Where the frequency of the WClkl4Ph<0> andClkTrkWClk4Ph<0> signals are the same, the counter circuits 152, 154will count in synchronicity. In some embodiments, the output signalsEnWrLvl<0:3> from the counter circuit 152 and EnWrLat<0:3> from thecounter circuit 154 change values at a frequency that is four times thefrequency of the Clk signal. A reset circuit 140 coupled to the countercircuits 152, 154 generates a reset signal RstGTree to reset the countof the counter circuits 152, 154 so that the counts of the two countercircuits 152, 154 correspond to one another in response to therespective clock signals.

Each of the counter circuits 152, 154 change the value of a binary digitof the count in response to the respective clock signal. For example,assuming that four-bit counter circuits are used for the countercircuits 152, 154, in response to a rising edge of the WClk4Ph<0> signalthe counter circuit 152 generates an output signal EnWrLvl<0:3>representing the binary number 1000. In response to a next rising edgeof the WClk4Ph<0> signal the counter circuit 152 generates an outputsignal EnWrLvl<0:3> representing the binary number 0100. The next binarynumber generated by the counter circuit 152 is 0010 and the followingbinary number is 0001. In response to the fifth rising edge of theWClk4Ph<0> signal the counter circuit 152 generates an output signalEnWrLvl<0:3> representing the binary number 1000. The counter circuit154 operates similarly in response to the ClkTrkWClk4Ph<0> signal andgenerates an output signal EnWrLat<0:3> representing the binary number.

The timing circuit 150 further includes a write latency multiplexer 156.The write latency multiplexer 156 delays the propagating WriteCmdYsignal to account for write latency and latches the WriteCmdY from thecommand decoder 116 in response to the EnWrLat<0:3> signal at a“position” corresponding to the value of EnWrLat<0:3>. The capturedWriteCmdY signal is then released from the write latency multiplexer 156as a write command enable signal WEn4<0:3> in response to a subsequentoccurrence of the EnWrLat<0:3> signal having the same value as itsrespective latched position. That is, if the EnWrLat<0:3> signal thatclocks the write latency multiplexer 156 is 0010, the WriteCmdY signalis latched into the 0010 position. At a subsequent occurrence of theEnWrLat<0:3> signal having a value of 0010, the WriteCmdY signal at the0010 position is released as a Wen4<0:3> signal. In some embodiments,the write latency multiplexer 156 has four positions and is implementedusing four latches, each latch clocked by one of the EnWrLat<0:3>signals.

FIG. 1B illustrates a write latency multiplexer 170 according to anembodiment of the invention. The write latency multiplexer 156 (FIG. 1A)may be implemented as the write latency multiplexer 170. The writelatency multiplexer 170 includes a write latency shifter 174 and a writelatency shifter 178. The WriteCmdY signal is shifted through a writelatency shifter 174 in response to the Clk2LatMux signal to provideappropriate delay due to write latency. As previously discussed, writelatency is the delay, in clock cycles, from the issuance of a writecommand to the latching of the first write data. Examples of typicalwrite latency are between 12 and 16 clock cycles of the Clk signal. Inan embodiment where a four clock cycle timing margin for synchronizingwrite data and propagation of a write command is used, the write latencyshifter 174 may provide between 8 and 12 clock cycles of delay. Afterbeing shifted through the write latency shifter 174, the WriteCmdYsignal is output to the write latency shifter 178 as the WriteCmdZsignal. The WriteCmdZ signal is captured by the write latency shifter178 in response to the EnWrLat<0:3> signals. The WriteCmdZ signal isreleased from the write latency shifter 178 as the WEn4<0:3> signal inresponse to the EnWrLat<0:3> signal having a value corresponding to theposition in which the WriteCmdZ signal was captured in the write latencyshifter 178. The resulting WEn4<0:3> signal has a value indicative ofthe latched position of the write command.

For example, in the previously discussed example, the WriteCmdY signalis provided to the write latency multiplexer 170 and is shifted throughthe write latency shifter 174 in response to the Clk2LatMux signal.After the WriteCmdY signal is shifted through the write latency shifter174 and is output as the WriteCmdZ signal, the write latency shifter 178captures the WriteCmdZ signal at a latched position determined by theEnWrLat<0:3> signal. In the previously discussed example, the WriteCmdZsignal is captured in response to a EnWrLat<0:3> signal of 0010. Thenext occurrence of the EnWrLat<0:3> signal having a value of 0010 willcause the write latency shifter 178 to output the captured WriteCmdZsignal as a corresponding write command enable signal WEn4<0:3> having avalue indicative of the latched position from which it was released. Inthe present example the WEn4<0:3> signal will have a value of 0010.

The released WEn4<0:3> signal is provided over a signal path 160 to awrite leveling flip-flop (FF) and control circuit 158. The signal path160 may introduce a propagation delay to the WEn4<0:3> signal as it istransmitted to the FF and control circuit 158. The propagation delay ofthe signal path may not be matched to a propagation delay of a writedata path over which write data is transmitted, as will be explained inmore detail below. The FF and control circuit 158 latches the WEn4<0:3>signal in response to the EnWrLvl<0:3> provided by the counter circuit152. Where the latched WEn4<0:3> signal includes an indication of awrite command, the FF and control circuit 158 generates an internalwrite enable signal WE. As will be described in more detail below, theWE signal can be used to time the latching of write data.

The WEn4<0:3> signal of a value is latched by the FF and control circuit158 in response to a EnWrLvl<0:3> signal having the same value. Forexample, in the previously discussed example where the WEn4<0:3> signalis released by the write latency multiplexer 156 in response to aEnWrLat<0:3> signal of 0010, the WEn4<0:3> signal arrives at the FF andcontrol circuit 158 after the propagation delay of the signal path 160and is latched by the FF and control circuit 158 in response to aEnWrLvl<0:3> signal having a value of 0010. As previously discussed, thecounter circuits 152, 154 count in synchronicity and provide outputsignals having the same value, thus, typically the EnWrLvl<0:3> signalof 0010 that latches the WEn4<0:3> signal is the next occurrence afterthe EnWrLat<0:3> signal of 0010.

In some embodiments, the FF and control circuit 158 is implemented as aset of flip-flops where each of the flip-flops is coupled to receive asingle bit of the WEn4<0:3> signal and clocked in response to one of thesignals of the EnWrLvl<0:3> signal.

FIG. 2 illustrates a data input circuit 200 according to an embodimentof the invention for one data node of a memory. That is, for a memoryhaving four input-output (IO) nodes, the data input circuit 200 isreplicated for each of the IO nodes. The data input circuit 200 includesa write data buffer and latch circuit 210 and write clock buffer andclock circuit 130 that provides write data and the write clock signalfor latching of the write data. The write clock buffer and clock circuit130 may be the same clock circuit as shown in FIG. 1A. The data inputcircuit 200 further includes a data register 230 that latches the writedata in response to the write clock signal and provides the latchedwrite data for writing to the memory array in response to a delayedinternal write enable signal WEDel. The WEDel signal is generated bydelaying the WE signal output from the write leveling FF and controlcircuit 158 through a delay circuit 240.

The write data buffer and latch circuit 210 includes a write data buffer212 that buffers the write data signals DQn to provide a buffered writedata signal DQIBOut. Write data latches 214, 216 capture the write dataand provide the data to the data register 230. The write clock bufferand clock circuit 130 include a write clock buffer 132 to generatecomplementary buffered write clock signals WClkIBOut, WClkIBOutF thatare provided to a multi-phase clock signal generator 134. As previouslydiscussed, a multi-phase clock signal generator generates various clocksignals having fixed phase relationships in response to an input clocksignal. In some embodiments of the invention, for example, theembodiment shown in FIG. 2, the multi-phase clock signal generator 130is a four-phase clock signal generator for generating quadrature clocksignals WClk4Ph<0:3>. In other embodiments of the invention, themulti-phase clock signal generator 134 may generate greater or fewerclock signals.

The multi-phase clock signals generated by the multi-phase clock signalgenerator 134 are used to clock data shift registers 232 of the dataregister 230 to capture the write data from the write data latches 214,216. In some embodiments, such as the embodiment illustrated in FIG. 2,four data shift registers 232 are clocked by a respective one of thequadrature clock signals generated by a four-phase clock signalgenerator. The data shift registers 232 provide latched write data to bewritten to the memory array in response to the WEDel signal providedfrom the delay circuit 240, which results from the WE signal generatedby the write enable timing circuit 150 (FIG. 1A).

A bank address store 10 is illustrated in FIG. 2. The bank address store10 releases a bank address for a write command so that the write datacorresponding to the write command is written to the correct bank ofmemory. The bank address store 10 releases the bank address for a writeoperation in response to the WE signal output by the write enable timingcircuit 150.

Operation of the timing circuit 100 circuit and the data input circuit200 will be described with reference to FIGS. 1 and 2, and the timingdiagram of FIG. 3. Generally, a WE signal that is used for latchingwrite data and providing the write data to be written to memory isgenerated by the write leveling FF and control circuit 158 for everywrite command latched by the write latency multiplexer 156. The WEsignal is generated in response to the EnWRLvl<0:3> signal when acorresponding write command enable signal WEn4<0:3> is provided to theFF and control circuit 158.

At time T0 (FIG. 3) a write command Wr-B0 to Bank0 of the memory arrayis received by the memory device. Although not shown in FIG. 3, theWr-B0 signal is buffered and decoded by the memory clock and commandbuffer and clock circuit 110 to be provided as a WriteCmdY signal to thewrite latency multiplexer 156. At time T1, the rising edge of theEnWrLat<0> signal clocks the write latency multiplexer 156 to latch theWriteCmdY signal corresponding to the Wr-B0 command. As previouslydiscussed, the latched WriteCmdY signal is shifted through a writelatency buffer (not shown) in the write latency multiplexer 156 toprovide appropriate delay due to write latency. For the present example,it is assumed the write latency is 12 clock cycles of the Clk signal andthe latched WriteCmdY signal is shifted through the write latency bufferfor eight clock cycles of the Clk signal. The write latency buffershifts the WriteCmdY signal in response to the Clk2LatMux signal (notshown in FIG. 3) and EnWrLat<0:3> generated in response to the Clksignal.

After shifting through the write latency buffer, the latched WriteCmdYsignal is then output by the write latency multiplexer 156 as a WEn4Y<0>signal in response to the rising edge of the EnWrLat<0> signal at timeT2. As previously discussed, the WriteCmdY signal that is latched by aparticular value of EnWrLat<0:3> signal is released as a WEn4Y signalfrom the write latency multiplexer 156 in response to an EnWrLat<0:3>signal having the same value at a later time. In the particular case ofthe Wr-B0 command, the corresponding WriteCmdY signal is latched by therising edge of the EnWrLat<0> signal, and consequently, is released asthe WEn4Y<0> signal in response to a later rising edge of the EnWrLat<0>signal.

The released WEn4Y<0> signal is propagated over the signal path 160 tothe write leveling FF and control circuit 158. As previously discussed,the signal path has an inherent propagation delay that delays thearrival of the released WriteCmdY signal. As shown in FIG. 3, theWEn4Y<0> signal arrives at the FF and control circuit 158 at time T3.The time difference between T2 and T3 represents the propagation delayof the signal path 160.

At time T4, the counter circuit 152 counts to a value equal to theEnWrLat<0> signal and the rising edge of the resulting EnWrLvl<0> signalcauses the WEn4Y<0> signal to be captured by the to the FF and controlcircuit 158. As previously discussed, the WEn4Y<0> signal released bythe write latency multiplexer 156 in response to the EnWrLat<0> signalis latched by the corresponding EnWrLvl<0> signal (i.e., the EnWrLvlsignal having the same value as the EnWrLat<0> signal). The capture ofthe released WEn4Y<0> signal in response to the EnWrLvl<0> signalresults in a HIGH transition of the WE signal output by the FF andcontrol circuit 158 at time T4.

The latching, release, and capture of write commands Wr-B1, Wr-B2, Wr-B3for memory banks 1, 2, 3 are similar to that previously described forthe Wr-B0 command. For example, at time T1 the Wr-B1 command is receivedby the memory device. The Wr-B1 command is buffered and decoded by thememory clock and command buffer and clock circuit 110 and provided tothe write latency multiplexer 156 as a WriteCmdY signal. The WriteCmdYsignal corresponding to the Wr-B1 command is latched at time T5 by therising edge of the EnWrLat<1> signal. As previously described, anearlier WriteCmdY signal corresponding to the Wr-B0 command waspreviously latched by the EnWrLat<0> signal at time T1.

The WriteCmdY signal for the Wr-B1 command is shifted through the writelatency buffer in response to the Clk2LatMux signal and EnWrLat<0:3>.After shifting through the write latency buffer, the latched WriteCmdYfor the Wr-B1 command is released from the write latency multiplexercircuit 156 as the WEn4Y<1> signal upon a later occurrence of the risingedge of the EnWrLat<1> signal at time T6. The released WEn4Y<1> signalpropagates over the signal path 160 and arrives at the FF and controlcircuit 158 at time T7. Upon the next occurrence of a rising edge of theEnWrLvl<0:3> signal having a value equal to the EnWrLat<1> signal, theWEn4Y<1> signal is captured by the FF and control circuit 158. At timeT8, the EnWrLvl<1> signal, corresponding in value to the EnWrLat<1>signal, causes the FF and control circuit 158 to capture the WEn4Y<1>signal and results in a HIGH transition of the WE signal at time T8.

The rising edges of the WE signal generated by the FF and controlcircuit 158 may be used to release latched write data, as will bedescribed in the operation of the data input circuit 200.

As previously discussed, the write latency for the present example isassumed to be 12 clock cycles of the Clk signal. That is, the write datafor a write command is provided to the memory device 12 clock cycles ofthe Clk signal after the corresponding write command is issued. It isadditionally assumed for the present example that the write clock WClkhas a frequency twice that of the Clk signal.

The first bit of the write data for the Wr-B0 command is provided attime T4 to the input data buffer and latch 210 (FIG. 2) and the bufferedwrite data is provided to the write data latches 214, 216. As known, thewrite data is provided to a input of the memory in serial fashion. Thus,the first bit of data is buffered and provided to both write datalatches 214, 216. However, the 0-degree clock signal (not shownseparately from the WClk signal in FIG. 3) generated by the multi-phaseclock signal generator 134 clocks only the corresponding data register232 of the data register 230 at time T4 to latch the first bit of datafrom the write data latch 214. The second bit of write data for theWr-B0 command is provided at time T9, buffered and provided to bothwrite data latches 214, 216. The 90-degree clock signal generated by themulti-phase clock signal generator 134 clocks only the correspondingdata register 232 at time T9 to latch the second bit of data from thewrite data latch 216. The third and fourth bits of write data for theWr-B0 command are provided and latched by a respective data register 232at times T10 and T11, respectively.

As previously discussed, the timing circuit 100 generates a WE signalhaving a HIGH transition in response to a WEn4Y signal being captured byan EnWrLvl signal having a same value as the EnWrLat signal thatreleases the respective WEn4Y signal from the write latch andmultiplexer 156. With respect to the HIGH transition of the WE signal inresponse to the capture of WEn4Y<0> signal (corresponding to the Wr-B0command) at time T4, the WE signal is delayed by the delay circuit 240(FIG. 2) to provide a WEDel signal at time T12 that is timed to releasethe four-bits of write data latched in registers 232 to be written tothe memory array. The bank address provided by the bank address store 10in response to the HIGH transition of the WE signal in response to theWEn4Y<0> signal released the bank address (bank 0 for the Wr-B0 command)to activate the appropriate memory bank for writing of the write datareleased by the data registers 232 in response to the WEDel signal.

The write data for the Wr-B1 command is handled in the same manner aspreviously described for the write data for the Wr-B0 command. Forexample, the first bit of the write data for the Wr-B1 command isprovided at time T8 to the input data buffer and latch 210 (FIG. 2) andthe buffered write data is provided to the write data latches 214, 216.The 0-degree clock signal (not shown separately from the WClk signal inFIG. 3) generated by the multi-phase clock signal generator 134 clocksonly the corresponding data register 232 of the data register 230 attime T8 to latch the first bit of data from the write data latch 214.The second bit of write data for the Wr-B1 command is provided at timeT13, buffered and provided to both write data latches 214, 216. The90-degree clock signal generated by the multi-phase clock signalgenerator 134 clocks only the corresponding data register 232 at timeT13 to latch the second bit of data from the write data latch 216. Thethird and fourth bits of write data for the Wr-B1 command are providedand latched by a respective data register 232 at times T14 and T15,respectively.

The HIGH transition of the WE signal in response to the capture ofWEn4Y<1> signal (corresponding to the Wr-B1 command) at time T8, the WEsignal is delayed by the delay circuit 240 (FIG. 2) to provide a WEDelsignal at time T16 that is timed to release the four-bits of write datalatched in registers 232 to be written to the memory array. The bankaddress provided by the bank address store 10 in response to the HIGHtransition of the WE signal in response to the WEn4Y<1> signal releasedthe bank address (bank 1 for the Wr-B1 command) to activate theappropriate memory bank for writing of the write data released by thedata registers 232 in response to the WEDel signal.

The write data for the Wr-B2 and Wr-B3 commands are handled in the samemanner as previously described for the write data for the Wr-B0 andWr-B1 commands.

In summary, clock signals from two different clock domains may be usedto latch write data of a corresponding write command by generating acorrectly timed internal write command signal WE used for capturingwrite data and providing the data to be written to the memory. Aspreviously discussed, conventional techniques rely on designing clocksignal paths for clock signals from two different clock domains to havesimilar propagation delays. This approach, however, is susceptible tovariations in process, voltage, and temperature. In embodiments of theinvention, the additional propagation delay experienced by the memoryclock is hidden from the write clock so that the power, voltage, andtemperature variations is not experienced by the write clock, and theclock signals can be synchronized.

The previous example described operation of the timing circuit 100 andthe data input circuit 200 where write data is provided to and latchedby the memory at four-times the frequency of the memory clock signalClk. However, in some embodiments of the invention, the frequency atwhich write data is latched by the memory is greater or less than thatpreviously described. Various modifications within the understanding ofthose ordinarily skilled in the art may be made in these embodiments.For example, where the frequency of the write data is n-times thefrequency of the Clk signal, in some embodiments of the invention themulti-phase clock signal generator 134 of the write clock buffer andclock circuit 130 generates n clock signals, and additionally, the dataregister 230 includes n data shift registers 232 to latch the writedata.

FIG. 4 illustrates a portion of a memory 400 according to an embodimentof the present invention. The memory 400 includes a write command-datatiming circuit 446 according to an embodiment of the invention, forexample, the write command-data timing circuit 100 of FIG. 1A. Thememory 400 includes an array 402 of memory cells, which may be, forexample, DRAM memory cells, SRAM memory cells, flash memory cells, orsome other types of memory cells. The memory 400 includes a commanddecoder 406 that receives memory commands through a command bus 408 andgenerates corresponding control signals within the memory 400 to carryout various memory operations. The command decoder further receives amemory clock signal CLK and a write clock signal WClk and generatesinternal clock signals for operation of the memory. Row and columnaddress signals are applied to the memory 400 through an address bus 420and provided to an address latch 410. The address latch then outputs aseparate column address and a separate row address.

The row and column addresses are provided by the address latch 410 to arow address decoder 422 and a column address decoder 428, respectively.The column address decoder 428 selects bit lines extending through thearray 402 corresponding to respective column addresses. The row addressdecoder 422 is connected to word line driver 424 that activatesrespective rows of memory cells in the array 402 corresponding toreceived row addresses. The selected data line (e.g., a bit line or bitlines) corresponding to a received column address are coupled to aread/write circuitry 430 to provide read data to a data output buffer434 via an input-output data bus 440. Write data are applied to thememory array 402 through a data input buffer 444 and the memory arrayread/write circuitry 430. A write command-data timing circuit 446according to an embodiment of the invention is coupled to the data inputbuffer and receives control/timing signals from the command decoder 406.The timing circuit 446 provides timing signals that are used to latchwrite data of a corresponding write command by generating a correctlytimed internal write command signal WE used for capturing write dataproviding the data to be written to the array 402. In some embodiments,the timing circuit 446 can provide timing signals for operation wherethe memory clock signal and the write clock signals are in two differenttime domains (e.g., different frequencies). The command decoder 406responds to memory commands applied to the command bus 408 to performvarious operations on the memory array 402. In particular, the commanddecoder 406 is used to generate internal control signals to read datafrom and write data to the memory array 402.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A write command and write data timing circuit, comprising: a firstcounter circuit configured to increment a first count in response to afirst count clock signal based on a write clock signal; a second countercircuit configured to increment a second count in response to a secondcount clock signal based on a memory clock signal; a write command latchcoupled to the second counter circuit configured to latch internal writecommands at a first time in response to the incrementing second countand configured to output the internal write command at a second timelater than the first time in response to the incrementing second counthaving a same value at the first time; a flip-flop (FF) circuit coupledto the write command latch and the first counter circuit and configuredto latch the internal write command delayed relative to the second timein response to the incrementing first count having the same value of thesecond count at the second time, the FF circuit further configured togenerate an internal write enable signal in response to latching theinternal write command; and a write data register configured to capturewrite data in accordance with the write clock signal and configured tooutput captured write data in response to the internal write enablesignal.
 2. The timing circuit of claim 1, further comprising: a inputclock buffer configured to receive the write clock signal and generate abuffered write clock signal in response; and a multi-phase clock signalgenerator configured to receive the buffered write clock signal andgenerate a plurality of clock signals having an equal phase relationshipwith one another, at least one of the plurality of clock signalssynchronized with the buffered write clock signal and at least one ofthe plurality of clock signals provided to the second counter circuit asthe second count clock signal.
 3. The timing circuit of claim 2 whereinthe write data register comprises a plurality of write data registers,each write data register clocked to latch write data in response to arespective one of the plurality of clock signals and release therespective latched write data in response to the internal write enablesignal.
 4. The timing circuit of claim 1 wherein the second countercircuit comprises a counter circuit configured to change each succeedingbit of the second count to a complement value in response to the secondcount clock signal.
 5. The timing circuit of claim 1 wherein the writecommand latch comprises a plurality of latches, each clocked by arespective bit of the second count.
 6. The timing circuit of claim 1wherein the write command latch comprises a buffer configured to shiftthrough the internal write command in response to a buffer clock signalderived from the memory clock signal to provide at least a portion of awrite latency.
 7. The timing circuit of claim 1, further comprising areset circuit coupled to the first and second counter circuits andconfigured to reset the first and second counter circuits simultaneouslyto a common reset value from which the first and second count values areincremented.
 8. A write command and write data timing circuit,comprising: internal write command latch configured to latch an internalwrite command in response to write command latch signal based on amemory clock signal, provide a latency delay to the latched internalwrite command, and release the latched internal write command inresponse to the write command latch signal; a write leveling flip-flop(FF) circuit coupled to the internal write command latch and configuredto latch the internal write command in response to an internal writecommand FF signal based on a write clock signal and generate an internalwrite enable signal in response to latching the internal write command;and a write data register coupled to the FF circuit and configured tocapture write data in response to the write clock signal and release thecaptured write data in response to a delayed internal write enablesignal.
 9. The timing circuit of claim 8, further comprising first andsecond counter circuits, the first counter circuit configured togenerate a first incrementing count value in response to the write clocksignal, the first incrementing count value provided to the FF circuit asthe internal write command FF signal, the second counter circuitconfigured to generate a second incrementing count value in response tothe memory clock signal, the second incrementing count value provided tothe internal write command latch as the write command latch signal. 10.The timing circuit of claim 9, further comprising a multi-phase clocksignal generator configured to generate a plurality of clock signals inresponse to the write clock signal, the plurality of clock signalshaving a clock frequency equal that of the memory clock signal.
 11. Thetiming circuit of claim 10 wherein the write clock signal has twice theclock frequency of the memory clock signal.
 12. A memory device,comprising; a memory array; a write data path coupled to the memoryarray and configured to couple write data to the memory array to bewritten; a command decoder configured to decode memory commands andgenerate internal write commands in response to receipt of a writecommand; a first counter circuit configured to increment a first countin response to a first count clock signal based on a write clock signal;a second counter circuit configured to increment a second count inresponse to a second count clock signal based on a memory clock signal;a write command latch coupled to the command decoder and to the secondcounter circuit, the write command latch configured to latch internalwrite commands at a first time in response to the incrementing secondcount and configured to output the internal write command at a secondtime later than the first time in response to the incrementing secondcount having a same value at the first time; a write leveling flip-flop(FF) circuit coupled to the write command latch and the first countercircuit and configured to latch the internal write command delayedrelative to the second time in response to the incrementing first counthaving the same value of the second count at the second time, the FFcircuit further configured to generate an internal write enable signalin response to latching the internal write command; and a write dataregister coupled to the write data path configured to capture write datain accordance with the write clock signal and configured to outputcaptured write data to the write data path in response to the internalwrite enable signal.
 13. The memory of claim 12, further comprising: ainput clock buffer configured to receive the write clock signal andgenerate a buffered write clock signal in response; and a multi-phaseclock signal generator configured to receive the buffered write clocksignal and generate a plurality of clock signals having an equal phaserelationship with one another, at least one of the plurality of clocksignals synchronized with the buffered write clock signal and at leastone of the plurality of clock signals provided to the second countercircuit as the second count clock signal.
 14. The memory of claim 13wherein the write data register comprises a plurality of write dataregisters, each write data register clocked to latch write data inresponse to a respective one of the plurality of clock signals andrelease the respective latched write data in response to the internalwrite enable signal.
 15. A method of latching a write command and writedata provided later than the write command, the method comprising:decoding a write command to generate an internal write command; latchingthe internal write command in response to a memory clock signal;releasing the latched internal write command after a latency delay inresponse to the memory clock signal and propagating the internal writecommand over a internal write command path; capturing write data inresponse to a write clock signal; latching the internal write commandfrom the internal write command path in response to a write clock signaland generating an internal write enable signal in response to thelatched internal write command; and releasing the captured write data tobe written to memory in response to the internal write enable signal.16. The method of claim 15, further comprising generating a firstlatching signal in response to the memory clock signal and generating asecond latching signal in response to the write clock signal, whereinlatching the internal write command comprises latching the internalwrite command in response to the first latching signal and whereinlatching the internal write command in response to a write clock signalcomprises latching the internal write command in response to the secondlatching signal.
 17. The method of claim 16 wherein generating a firstlatching signal comprises generating a first count value and generatinga second latching signal comprises generating a second count value, thefirst count value incrementing in response to the memory clock signaland the second count value incrementing in response to the write clocksignal, the first and second count values incrementing in synchronicity.18. The method of claim 17, further comprising resetting the first andsecond count values to a common reset value before incrementing of thecount values begins.
 19. The method of claim 17 wherein generating thefirst count value comprises generating a count value incrementing byshifting a bit value different from the other bits of the count to asucceeding bit position in response to the memory clock signal.
 20. Themethod of claim 17 wherein latching the internal write command inresponse to the first latching signal comprises latching the internalwrite command in response to the first count value having a latch valueat a first time and wherein releasing the latched internal write commandafter a latency delay in response to the memory clock signal comprisesreleasing the latched internal write command after the latency delay inresponse to the first count value having the latch value at a secondtime later than the first time.
 21. The method of claim 20 whereinlatching the internal write command from the internal write command pathin response to a write clock signal comprises latching the internalwrite command from the internal write command path in response to thesecond count value having the latch value at a time after the release ofthe latched internal write command.
 22. The method of claim 15 whereincapturing write data in response to a write clock signal comprisescapturing different write data in response to a transition of the writeclock signal and releasing the captured write data to be written tomemory in response to the internal write enable signal comprisesreleasing the captured different write data simultaneously in responseto the write enable signal.
 23. The method of claim 22, furthercomprising generating a plurality of clock signals having a fixed phaserelationship with one another and wherein capturing different write datain response to a transition of the write clock signal comprisescapturing respective write data in response to a rising edge of arespective one of the plurality of clock signals.